Crimpable, composite nylon filament and fabric knitted therefrom



Aug. 27, 1968 H. OLSON 3,399,108

CRIMPABLE, G OSITE NYLON FI ENT AND FA IC KNITTED THEREF Filed June 18, 1965 3 Sheets-Sheet 1 Filed June 18, 1965 H. OLSON J OSITE NYLON FILAMENT AND KNITTED THEHEFROM 3 Sheets-Sheet 2 Aug. 27, 1968 I E. H. OLSON CRIMPABLE, COMPOSITE NYLON FILAMENT AND FABRIC KNITTED THEREFROM Filed June 18, 1965 3 Sheets-Sheet 5 I --1zo United States Patent ABSTRACT OF THE DISCLOSURE A crimpable composite filament in which one component is a crystalline homopolyamide and the other a nonisomorphic random copolyamide containing at least of two polymer units. Its high crimp retractive force leads to improvements in stretch hosiery.

This application is a continuation-in-part of my copending application Ser. No. 335,187, filed Jan. 2, 1964, now abandoned, which is a continuation-in-part of my copending application Ser. No. 202,611, filed June 14, 1962, now abandoned, which is a continuation-in-part of my abandoned application Ser. No. 132,449, filed Aug. 18, 1961. The invention relates to polyamide filaments.

Polyamide filaments have been predominant in the filed of womens hosiery for many years, having almost completely displaced silk and other fibers in this market. Although the present product is excellent in most respects, there is a need for improvement, especially in connection with such factors as appearance, fit and comfort. This need arises from the fact that the standard sizes of seamless hose which are available do not provide a good and satisfactory fit for all wearers. In many cases, the hose which provides a good fit for one part of the leg does not provide an adequate fit in other places, e.g., if the hose fits properly at the ankle, the knee will be too tight. These factors have led to the production of stretch hose which provide improvement in fit and comfort due to their ability to give enough to fit the larger parts of the leg without discomfort. However, such hose must originally be quite small to achieve the desired fit and thus are unattractive in appearance to the purchaser as compared to regular nonstretch hose. In actual use, stretch hose are lacking in stitch clarity and have a rather coarse appearance when compared with regular nonstretch hose.

According to one known procedure, stretch hose are knitted from single-component filaments which are crimped in advance by passing them over a heated surface whereby one side of the filament acquires a lower shrinkage than the other side. In addition to aesthetic deficiencies, many difficulties are encountered in achieving uniform filament properties. Consequently, the amount of waste yarn is excessive and yarn costs are comparatively high.

Composite, two-component filaments which crimp when heated are well known in the art. However, known filaments of this type do not crimp adequately under the restraint imposed in a fabric to achieve the objectives of this invention unless highly dissimilar polymers which eventually tend to separate are used in the respective components.

The most important object of the present invention is to provide two-component polyamide filaments suitable for use in the production of fabrics. Another important object is to provide composite filaments which may be used to produce stretch type hosiery of improved fit and ice comfort while retaining the desirable appearance and performance characteristics of nonstretch nylon hose.

The above objects have been accomplished with a crimpable composite nylon filament consisting of two continuous, adherent, eccentric components, one component consisting essentially of a crystalline, a fiber-forming homopolyamide, the other component consisting essential- 1y of a nonisomorphic, fiber-forming, random copolyamide containing at least 20% by weight of each of two polymer units from which the copolyrner is prepared. When polymer unit combinations are selected and the filaments are processed in accordance with the teachings of the present invention, the nonisomorphic copolyamide component is characterized by equatorial X-ray reflections similar to those exhibited by the crystalline homopolyamide. The filaments have the further characteristic of crimping helically with the copolyamide component as the load bearing member when subjected to steam, the crimp retractive force being sufficient to cause the filament to crimp when under a slight tension, e.g., when in a fabric. For use in hosiery leg yarn, the monofils should retract by at least 12% of their length upon exposure to C. steam at atmospheric pressure (hereinafter referred to as atmospheric steam) while under a restraint of 0.0012 g.p.d. They should have a retraction due to crimping of at least 24% upon exposure to a 118 C. steam atmosphere while under a restraint of 0.0012 g.p.d.

Preferably, the eccentric filaments, after crimping at a steam temperature of 118 C., have a crimp diameter of about 6 or 7 to 15 mils and the helices are spaced apart by a distance of 16 to 70 mils or within the narrower rangers of 16 to 50 or 24 to 70 mils. For hosiery monofils, the optimum range is 7 to 11 mils diameter and 16 to 38 mils spacing or the smaller range of 24 to 38 mils spacing.

The process of the present invention comprises extruding the homopolyamide and random copolyamide components in eccentric relationship to form a composite filament, drawing the filament under conditions such that the homopolyamide component becomes crystalline and oriented and subsequently relaxing while simultaneously heating the filament, thus producing a crimped composite structure in which both components exhibit the equatorial X-ray reflections characteristic of a crystalline homopolyamide. Both components must be of fiber-forming molecular weight to give the desired level of processability and fiber properties. Preferably, the filaments are heated with little or no tension applied in the heating-relaxing step, cooled as they advance through a room temperature environment and then stretched to remove crimp induced by differential shrinkage in the heat relaxation step. The time-temperature relationship of the heat relaxation step is sufficient to produce the desired X-ray diffraction appearances in the nonisomorphic copolyamide component. For this purpose, a temperature of at least C., but below the softening point of either component, is applied for a sufficient period of time to permit the filament to crimp to the desired extent.

When reheated, the stretched filaments disclosed herein have suificient crimping force to develop crimp after having been incorporated into a hose fabric and to thereby impart stretchability to the hose. Known composite nylon filaments with a nonisomorphic copolyamide as one component do not crimp with sufficient force to overcome fabric resistance and impart adequate stretchability.

In some instances, the components in the filament are extruded in side-by-side relation since this structure provides the maximum crimp retractive force. However, where the maximum degree of eccentricity is achieved in a sheath-core arrangement and the polymer system and processing conditions are optimum, adequate crimp retraction under restraint may be achieved to permit its use in hose leg yarn. For hosiery welt yarns, two-component sheath-core filaments having a retraction of at least 7% in atmospheric steam under 0.0012 g.p.d. load are satisfactory. As used herein, the term eccentrid is meant to include both side-by-side and truly eccentric sheath-core structures.

' Other objectives and advantages will be apparent from the following specification and examples wherein reference is made to the accompanying drawings in which:

FIGURES 1 and 4 are schematic representations of equipment which was used in processing the spun filaments exemplified hereinafter; and

FIGS. 2 and 3 are fragmentary transverse sectional views of spinnerets employed in the spinning step.

The expression relative viscosity as used herein signifies the ratio of flow time in a viscometer of a polymer solution containing 8.2- 0.2% by weight of polymer relative to flow time of the solvent by itself. Measurements of relative viscosity are made with 5.5 grams of polyamide in 50 ml. of formic acid at 25 C.

The X-ray measurements referred to herein may be made in the following manner. The composite filaments are exposed on a Hilger semi-micro-focus diffraction unit using a flat plate Norelco micro-camera similar in design to that described by Fankuchen and Mark, J. Applied Physics 15, 364 (1944). Side-by-side composite filaments are mounted in the camera, with the aid of a microscope, in such a manner as to place only one component in the path of the X-ray beam. In the case of eccentric sheathcore filaments, the filament is mounted so that the X-ray beam passes through only one half, or preferably somewhat less than one half, of the filament. If the microscopic technique should prove unsatisfactory, the filament is then rotated 45 around its long axis and the measurement re peated. This is continued until eight measurements have been made. If any one of these measurements indicates a lack of crystallinity, the measurements should be repeated. If confirmed, the measurement indicates that one of the components does not have the required crystallinity.

The degree of crystallinity is determined from radial densitometer traces along the equator of the X-ray diagram. Such a trace, for a polyamide with well-developed 100 and 010, 110 reflections, will show two distinct peaks. As the degree and perfection of crystallinity decreases, these peaks move together and broaden. For samples of very low crystallinity, they merge into a single peak. A parameter indicating crystal perfection is the ratio of the equatorial distance of separation of the outside peaks (010, 110 planes) to the equatorial distance of separation of the inside peaks (100 plane). When this peak ratio becomes less than 1.10, some difiiculty may be encountered in determining the ratio with a high degree of accurary.

As discussed more fully hereinafter, some copolyarnides may not develop a truly crystalline structure but do develop a crystal-like structure which gives the equatorial X-ray reflections characteristic of a truly crystalline structure. It is to be understood that where reference is made to crystalline structure, such crystal-like structures are meant to be included, i.e., any structure which gives equatorial X-ray reflections characteristic of a crystalline structure is considered to be crystalline for the purposes of this invention.

Crystallite dimensions are also reported in the examples. These are estimated from the breadth of the refiection on the equatorial radial traces for the lateral crystal dimension (010, 110 and 100) and from the breadth of the 015 reflection on a radial meridional trace for crystallite length. The respective dimensions are computed from measurements made in these traces using the Scherrer equation and the procedure outlined by H. P. Klug and L. E. Alexander, X-ray Diffraction Procedure, John Wiley and Sons, Inc., New York, N.Y., chapter 9.

The orientation angles reported were taken from azimuthal densitorneter traces through the equatorial reflections (010, 110 and 100). The values are calculated fro the width of the respective areas at half maximum intensity and have been determined according to the procedure outlined by H. G. Ingersoll, J. Applied Physics 17, 924 (1946).

EXAMPLE I An evaporator is charged with 296 pounds of a 36.2 percent aqueous solution of hexamethylenediammonium sebacate- (6-10 salt solution prepared from hexamethylene diamine and sebacic acid, the sebacic acid containing about 8% by weight of a mixture of undecanedioic and dodecanedioic acids as impurities) and 225 pounds of a 48.9% aqueous solution of hexamethylenediammonium adipate (6-6 salt solution) and 159 pounds of water are removed by evaporative heating at atmospheric pressure. After adding 230 grams of aqueous acetic acid solution to the salt solution as a viscosity stabilizer, the solution is transferred to an autoclave, heated to a temperature of about 210 C. and brought to a pressure of 250 p.s.i.g. At this point, 1295 grams of a 20% aqueous slurry of titanium dioxide are added. The solution is then heated at 250 p.s.i.g. for a period of 3 hours, the temperature increasing to 274 C. during this time. Pressure is reduced over a period of 130 minutes to atmospheric and the temperature is increased to 279 C. The polymer is then held for 60 minutes at this tempreature, extruded under 75 p.s.i.g. nitrogen in the form of a ribbon, quenched on a water cooled casting wheel and cut into inch flakes in the conventional manner. The nonisomorphous copolymer consisting of 50% polyhexamethylene adipamide and 50% polyhexamethylene sebacamide/undecanedioamide/ dodecanedioamide has a relative viscosity of 54.

Polyhexamethylene adipamide (6-6 nylon) flake having a relative viscosity of 45 is prepared in the conventional manner. The two flakes (6-6 and 6-6/ 610/ 6-11/ 612) are melted separately and pumped to a spinneret assembly of the type shown in FIG. 2. This assembly includes a block 10 provided with a first ringshaped cavity 12 and a second cavity 14. Each cavity discharges through one of the passages 16, 18 to each of the several holes 20 in spinneret plate 22. The spun filaments are air quenched and each is wound into a package 24 (FIG. 1) in the conventional manner. The filament 26 is subsequently withdrawn from the package, drawn to a ratio of 5.3 over a draw pin 28 heated to 105 C. and passed from the draw roll 30 through a pair of meshing nylon gears 32. As shown in FIG. 1, these gears are rotated by means of an air jet and function to pull the drawn yarn from the draw roll, to prevent back wrapping and to feed the yarn into a crimping chamber 34 where low tension exists. In chamber 34, the yarn is crimped into helical form by a jet of heated air which is controlled in such a manner as to give an air temperature of 155 C. at the chamber exit. The yarn is then passed through an eyelet in a batfie plate 36 which functions to deflect most of the hot exhaust air away from a cold air aspirator 38. The yarn is then cooled by passing it through aspirator 38 in which room temperature air is drawn over the yarn. Form the cold air aspirator, the crimped yarn is led through a lower guide 40 and then around four snubbing pins 42 where tension is applied to remove the crimp before the yarn passes around withdrawal roll 44 to package 46. It is permitted to retract by 22% of its as-drawn length between draw roll 30 and withdrawal roll 44.

A skein of the 15 denier monofil is prepared by winding loops to give a 1500 denier skein of about cm. length when suspended with a weight attached. The skein is hung on a hook with a 500 gram weight (0.33 g.p.d.) suspended from its other end. After one minute, the length (a) of the skein is measured and found to be 55.8 cm. The 500 gram load is removed and a 1.8 gram load is applied in its place so that the skein is under a tensile load of 0.0012 g.p.d., i.e., a tension slightly in excess of that on the yarn when knitted into a fabric. Steam at atmospheric pressure is then applied over the entire length of the skein for one minute and the skein is allowed to dry in air for minutes, after which the skein length (b) is measured and found to be 43.3 cm. The retraction in length is due to the initial shrinkage of both components followed by additional shrinkage of the copolyamide component which results in the development of a spiral crimp. The 1.8 gram load is then removed, a 500 gram load is again applied for one minute and the length (0) of the skein again determined and found to be 55.0 cm. The crimp retraction and shrinkage of the filament are then calculated as follows:

Crimp retraction, percent 100XT=100X 55 =21.3

. ac 55.855 Shrinkage, percent-- 100 X 100 1.43

For purposes of comparison, it is noted that drawn denier monofils of the same composition which have not been heat relaxed were tested in atmospheric steam and found to have crimp retractions ranging from 1-5%. hose knitted from monofils having such a low level of crimp retraction would not show any appreciable improvement in fit and comfort over available hose of conventional construction.

In another test, crimp retraction of 22% heat relaxed filaments of the same composition is determined according to the same procedures except that the skein, bearing the 1.8 gram load, is subjected to steam at 118 C. (245 F.) in a conventional hosiery boarding oven. Under these conditions, the crimp retraction is 32.5% and the shrinkage is 8%. The helix spacing and diameter of these filaments are measured under a tension of 0.0012 g.p.d. by taping one-inch lengths of the crimped, tensioned skein on a microscope slide and projecting the magnified image on a grid covered screen by means of a projection microscope. The average helix diameter is found to be 9 mils and the average spacing of the helices is 26 mils.

Forty total denier, 13-filament crimpable yarn is prepared as described above except that the draw ratio is 3.82, the drawpin temperature is 98 C. and the yarn is permitted to contract only 18% in the relaxation step. This yarn has a crimp retraction of about 6.5% in atmospheric steam. Since it is used in the welt, heel and toe of the hose, the higher crimp retraction possessed by the 22% relaxed monofilaments is not required.

X-ray measurements on each component of the 22% relaxed Composite filaments are made as previously described. Values, where determinable, for filaments after drawing as well as after heat treatment, cooling and stretching, are reported in the following table:

1 Crystal structure too imperfect to measure.

The 100 and 010, 110 peaks on the densitometer trace were separated to some extent in the case of the 66 component after drawing, as signified by the peak ratio of 1.092 which indicates a substantial degree of crystallinity. No separationof the peaks occurred in the case of the copolymer component after drawing, as signified by the 1.00 ratio which indicates a very low degree of crystallinity. After the relaxed heat treatment however distinctly separate peaks were observed as indicated by the higher ratios. The tabulated increase in crystal dimensions is also indicative of a substantial degree of crystallinity.

Womens hose are knitted using the 15 denier monofil, except in the welt, heel and toe where the 40 total denier 13 filament yarn is employed. The course count, as measured on a volumetric hose board, is kept in the range of 45 to 70 courses per inch over the knee, calf and ankle sections of the hose. The hose feet are knitted /2 size larger than the finished size desired. The hose are wrapped loosely in cheese cloth, boiled off in hot water for ten minutes and put on a hose board. It is found that when a standard hose board is used the resultant hose is narrower than desired. This condition is corrected by boarding on a standard board and measuring the resulting width at the various parts of the hose. The ratio of standard board width to hose width obtained is then multiplied by the desired hose width to give the board width required at this location in the hose. It is also found that the optimum boarding length is 45 inches shorter than the knitted length. Boards are then constructed to this design and the hose placed on the board and steamed for 10 minutes with 5 p.s.i.g. steam. The manner in which the hose shrink to the board is indicative of the extent of crimp retractive force developed in the two-component filaments. The hose are dyed in the conventional manner, placed while damp on the hose board and steamed as before.

The finished hose are somewhat similar in appearance to nonstretch hose although slimmer and slightly shorter but have the fit and comfort of stretch hose. The clarity of stitch is greatly superior to that of stretch hose so that the hose of this invention have a much better appearance when displayed for sale, as well as on the wearers leg.

The two components of each filament adhere sufficiently to prevent filament splitting and the resultant undesirable effects when the hose are placed in use.

EXAMPLE II Example I is repeated except that the ratio of salts used in the polymerization step is adjusted to produce a copolymer containing 60% polyhexamethylene adipamide and 40% polyhexamethylene sebacamide. When tested, crimp retraction is substantially the same as in Example I. Results of X-ray examination and hosiery tests are also substantially the same as in Example I. Similar results were also obtained with a copolymer containing 40% polyhexamethylene adipamide and 60% polyhexamethylene sebacamide. The relative viscosities are in the same range with that of the copolymer in Example 1.

EXAMPLE III Example I is repeated except that the pin 28 is only heated to 40 C. and the yarn is passed at a speed of 843 y.p.m. upwardly from draw roll 30 through an inverted crimping chamber 34, carried through the crimping chamber by the hot air stream, advanced over a pin located at about the same position as gears 32 (FIG. 1), which are omitted, and then passed downwardly to guide 40, the baffle plate 36 and aspirator 38 being omitted. From guide 40, the yarn advances as shown in FIG. 1. Air temperature at the exit of the inverted chamber 34 is C. and the yarn is permitted to retract 22% between draw roll 30 and withdrawal roll 44. Between snubbing pins 42 and roll 44, it is placed under tension to remove the crimp. Cooling of the yarn is achieved in the room temperature environment between crimping chamber 34 and snubbing pins 42. When the yarn is tested as described in Example I, the results are substantially the same except that the crimp retraction under 0.0012 g.p.d. load is 14.4% with atmospheric steam and 27% with 118 C. steam.

When the above procedure is repeated except that the yarn is passed directly from the guide pin above the inverted chamber 34 to and over one of the pins 42 and thence directly to windup package 46 where the yarn is wound at a tension of 35 grams, the crimping action in the heated zone is largely eliminated and the resulting yarn has a crimp retraction in atmospheric steam of only 56%. Hose from this yarn do not provide a satisfactory fit.

EXAMPLE IV A two-component filament is extruded and processed as described in Example I except that polycaproamide (6 polymer) of 45 relative viscosity is substituted for the 66 homopolymer component. The results are substantially the same except that the shrinkage is about 2% and the crimp retraction under 0.0012 g.p.d. is about 20% with atmospheric steam and about 33% with 118 C. steam.

EXAMPLE V A 48% aqueous solution of hexamethylene diammonium adipate (66 nylon salt) is charged to an evaporator. A 40% aqueous solution of hexamethylene diamm-onium isophthalate (6-I), prepared by combining equimolar proportions of hexamethylene diamine and isophthalic acid, is added to the evaporator in sufficient amount to provide 27% by weight of hexamethylene diammonium isoph thalate based on the total Weight of dry salt present. The salt solution is then evaporated to a 75% concentration level, at which point the temperature is about 138 C. The 75 salt solution is charged to an autoclave and heated to a temperature of about 242 C. and 250 p.s.i.g. pres sure, about 85 to 90 minutes being required for this operation. The pressure is then reduced over a period of 85 minutes to atmospheric pressure and the temperature is increased to 270-275 C. The copolymer is held for 40 minutes at this temperature, extruded in the form of a ribbon, quenched on a water-cooled casting wheel and cut into /2 inch flakes in the conventional manner. The copolymer has a relative viscosity of 39.

6-6 nylon flake prepared as described in Example I and the 66/6-I flake are melted separately, extruded together to form side-by-side filaments which are quenched, wound, subsequently withdrawn from the package, drawn to denier at a ratio of 4.67, crirnped by heating under low tension, cooled and stretched to remove the crimp, all as described in Example I.

The filaments are then crimped While under a tension of 0.0012 g.p.d. and the crimp retraction, determined as in Example I, is found to be in atmospheric steam and 34.5% in 118 C. steam. The shrinkage of the filament in 100 C. steam is 5%. The shrinkage of the filament in boiling water in a relaxed state is 10%. When hose are knitted and treated, the results are substantially the same as observed in Example I,

X-ray measurements are made on each component of the composite filament, as in Example I. The results, reported in Table II below, indicate that both components, after relaxed heat treatment, show the equatorial X-ray reflections which are characteristic of crystalline homopolyamides.

1 Crystal stlucture too imperfect to measure.

EXAMPLE VI After charging an evaporator with 3230 g. of a 35.0%

aqueous solution of hexamethylenediammoniurn dodecanedioate (6-12 salt solution) and 2360 grams of a 48.5%

aqueous solution of hexamethylenediammonium adipate (66 salt solution), 1780 grams of water are removed by evaporative heating at atmospheric pressure. The solution is then transferred to an autoclave, heated to a temperature of 215 C. and brought to a pressure of 250 p.s.i.g. At this point, 35 grams of a 20% aqueous slurry of titanium dioxide are added. The solution is then heated at 250 p.s.i.g. for a period of two hours, the temperature increasing to 270 C. during this time. The pressure is reduced over a period of sixty minutes to atmospheric and the temperature is increased to 278 C, The polymer is then held for 60 minutes at this temperature, extruded under p.s.i.g. nitrogen to form a ribbon, quenched on a water-cooled casting Wheel and cut into flake in the conventional manner. The copolymer consisting of 50% polyhexamethylene dodecanediamide units and 50% polyhexamethylene adipamide units has a relative viscosity of 53.

The above flake (66/612) and polyhexamethylene adipamide (66) flake were then spun as side-by-side two-component filaments, drawn, heat-relaxed, cooled and stretched, as described in Example I. Crimp retraction and shrinkage values substantially equivalent to those of Example I were obtained.

X-ray measurements on the 6-6/612 and the 6-6 components were made separately as previously described. The values for these two-component filaments show essentially the same relationship as between the 66 and 66/6-10 filaments of Example I, The degree of crystallinity of the 6-6/6-12 filament has been changed from low up to a satisfactory level.

The crimp retraction in atmospheric steam is 17.4% and in 118 C. steam is 32%.

Womens hose were knit and treated in a manner similar to Example 1, except that they were treated with atmospheric steam rather than hot water before boarding. They displayed the advantages in appearance, fit and comfort shown in Example I.

EXAMPLE VII An evaporator is charged with 370 gallons of an aqueous solution of hexamethylenediammonium sebacate (6-10 salt solution prepared as in Example I) containing 1,132 pounds of dry salt and 260 gallons of an aqueous solution of hexamethylenediammonium adipate (66 salt solution) containing 1,163 pounds of dry salt and the resulting solution is heated at 13 p.s.i.g, until the temperature reaches 132 C., giving a salt concentration of approximately 75 The solution is then transferred to an autoclave, heated to a temperature of about 205 C. and brought to a pressure of 250 p.s.i.g At this point, sufficient 20% aqueous titanium dioxide slurry is added to give a concentration of 0.3% TiO in the final polymer. The solution is then heated at 250 p.s.i.g. until the temperature reaches 225 C, The pressure is then reduced over a period of minutes to atmospheric and the temperature is increased to 250 C. The polymer is then held, at atmospheric pressure, for 30 minutes at a temperature of 250-260 C., extruded under p.s.i.g. nitrogen in the form of a ribbon, quenched on a water-cooled casting wheel and cut into Az-inch flake in the conventional manner. The copolymer, consisting of 50% polyhexamethylene adipamide and 50% polyhexamethylene sebacamide, has a relative viscosity of 45.

Polyhexamethylene adipamide (66 nylon) flake having a relative viscosity of 46.5 is also prepared in the conventional manner. The two flakes (66 and 66/ 6-10) are fed separately to a dual screw melter Where the flake is first conditioned by exposure to humidified nitrogen at 125 C. and then melted and pumped to a spinneret assembly of the type shown in FIGS. 3 and 4. The relative viscosity of the 6-6 flake after conditioning is 50 and that of the 66/610 copolymer flake is 55. The melt temperature of the 6 6 is 290 C. and that of the 6-6/6-10 is 282 C. The two polymers are extruded, with the 66/ 6-10 copolymer as the core, to form eccentric sheath-core hosiery monofils containing equal amounts of the copolymer and homopolymer. The sheath, at its thinnest point, has a thickness equivalent to about 1% of the total filament diameter. The clearance between the projection 135 on pack 130 and spinneret plate 142 is 0.003 inch. The filaments are set by quenching, using a 60-inch chimney and an air temperature of 45 C., steam conditioned as described in US. Patent No. 2,289,- 860 and each is wound into a package 114 (FIG. 4) at 461 y.p.m. That monofil is subsequently withdrawn from the package and drawn to a ratio of 4.95 over an unheated draw pin 118 situated between rolls 116 and 120 to give a final denier of 15. It is passed from the second draw roll through a tubular crimping chamber 122, three inches in length, at 563 y.p.m. In the chamber, the monofil is heated by passing 0.5 cubic feet/minute of heated air at 3038 p.s.i.g. through the chamber to give an air temperature of 20l-208 C. at the exit. The yarn which is under low tension in the crimping chamber is crimped into helical form as indicated at 123 and then led over snubbing pins 124 and 126 to remove the crimp by stretching the yarn slightly. The crimpable monofil is then wound into a package 127. The relative speeds of rolls 120 and 128 permit 22% retraction in the length of the yarn between these points.

When yarn from package 127 is exposed to hot water or steam it crimps in a very uniform fashion and the crimp diameter and crimp elongation are quite uniform. The crimp retraction at a load of 0.0012 g.p.d., determined as described in Example I, is 14% in atmospheric steam and 27.5% in 118 C. steam. The average crimp spacing and diameter, measured as in Example I, are about 8.5 mils and 27 mils, respectively. When the yarn is knit into womens semi-stretch hose, in combination with 45 denier, 7 filament welt yarn having 13.5% crimp retraction in 118 C. steam, the hose have a very uniform texture and perform well, being similar to the hose of Example I in fit and appearance. When the crimp retraction test at 118 C. is applied to the drawn filament before the relaxed heat treatment, the retraction under 0.0012 g.p.d. load is only 16.6%. In addition, hoisery fabric knit from monofil which has not been subjected to the relaxed heat-treatment has a very poor appearance as compared to fabric from monofil prepared as described above. When the monofil is passed through the heated chamber at constant length as taught by the prior art, the crimp retraction is reduced to 6.5%. Treatment of this filament in a relaxed state with steam at 102 C. increases the crimp retraction to its original level of 16.6%, but does not produce a filament satisfactory for the purposes of this invention.

EXAMPLE VIII An evaporator is charged with 2,345 lbs. (1062 kg.) of a 49.5% aqueous solution of hexamethylenediammonium adipate (66 salt solution) and 3,635 lbs. (1648 kg.) of a 31% aqueous salt solution prepared by reacting equimolar proportions of hexamethylenediamine and a mixture of acids prepared by adding 15% by weight of dodecanedioic acid to technical grade sebacic acid which contains about 2% by weight of undecanedioic acid and about 3% by weight of dodecanedioic acid. The salt solution is then evaporated to a 75% concentration level,

at which point the temperature is about 132 C. at a pressure 13 p.s.i.g. (0.91 kg./sq. cm.). The salt solution is charged to an autoclave and heated to a temperature of about 210 C. and brought to a pressure of 250 p.s.i.g. (17.6 kg./sq. cm.). At this point 30 lbs. (13.6 kg.) of a 20% aqueous slurry of titanium dioxide is added. The solution is then heated to a temperature of about 225 C. at 250 p.s.i.g. (17.6 kg./sq. cm.) pressure, about 60 minutes being required for the heating operation. The pressure is then reduced over a period of minutes to atmospheric pressure and the temperature is increased to 260-265 C. The copolymer is held for 30 minutes at this temperature, extruded in the form of a ribbon, quenched on a water-cooled casting wheel and cut into /2" (1.27 cm.) flake in the conventional manner. The copolymer has a relative viscosity of about 46.

Following the procedure of Example VII, sheath-core monofil is prepared with the copolymer, prepared as above, as the core and 6-6 flake having a relative viscosity of about 46 as the sheath. The crimp retraction of the monofil at a load of 0.0012 g.p.d., determined as described in Example I, is 32.5% in 118 C. steam. The crystallinity of the core is found to be similar to that of the sheath. The crimp spacing and diameter, determined as described in Example 1, are 25 mils and 8.5 mils, respectively.

When the monofil is made into womens miniature hose and finished at 118 C., the hose are found to provide improved fit for various leg sizes as compared to womens semi-conventional hose and are superior in appearance on the leg as compared to conventional stretch hose. The miniature hose prepared from the monofil of this example are found to be superior to similar hose prepared from the monofil of Example VII with regard to improved fit.

EXAMPLE IX Example VII is repeated except that the ratio of the copolymer to homopolymer is varied to give 60% core and 40% sheath in one test and 70% core and 30% sheath in another. The 60:40 ratio filaments exhibit a crimp retraction at 118 C. of 32.4% while the 70:30 ratio gives a retraction of 34.2%.

EXAMPLE X Nylon 66 flake having a relative viscosity of 36.5 and 6-6/6-I flake having a relative viscosity of 29.3 and containing 30% of 6-1 (polyhexamethylene isophthalamide) are prepared following the procedure of Example V. Following the procedure of Example VII, the 6-6 and 6-6/6-1 flake are extruded to form a sheath-core monofil with the 66 polymer as the sheath, drawn, heat-treated and wound into a package. The draw ratio is 4.6 and the air temperature at the crimping chamber exit is C. When the monofil contains 50% sheath and 50% core, the crimp retraction .at 118 C. is 26.4%. When the flow of 66 and 6-6/6-1 polymers is adjusted to give 60% core and 40% sheath, the crimp retraction at 118 C. is 30.2%. When the monofil is knit into womens semi-stretch hose, the results are substantially the same as found for the hose of Example I. The monofil having 60% core is also knit into womens miniature stretch hose. These hose are found to provide excellent fit for various leg sizes and are superior in appearance on the leg as compared to conventional stretch hose.

It has been found that two-component filaments are greatly improved with respect to their utility in fabrics, particularly hosiery fabric, when one component is a crystallizable homopolyamide and the other component is a crystallizable random copolyamide containing at least 20% by weight of each of two polymer units and the filaments are heat treated in a relaxed state to produce in both components X-ray diffraction patterns characteristic of a crystalline homopolyamide. This improved utility and other advantages of the filaments of the present invention are apparent from the foregoing examples. Nonisomorphic copolyamides must be employed since isomorphic copolymers are similar in behavior to homopolymers and do not shrink enough to give the desired crimping.

Filaments which are particularly suitable for the production of hosiery are produced by adjusting the relative amounts of polymer units in the copolyamide so that the crimp retraction and retractive force are in the desired range. For this purpose, the copolymer should contain at least of each of two polymer units. For optimum results, the 6-6/6-10 copolymer should contain -70% of the 6-6 polymer units while the 6-6/6-12 copolymer should contain -60% of the 6-6 units and the 6-6/6-1 copolymer should contain -80% of the 6-6 units. The optimum compositions for other copolyamides within the scope of this invention can readily be determined by one skilled in the art.

For the production of sheath-core filaments for use in the preparation of miniature stretch hose, it may be desirable that the copolymer contain more than two polymer units. Thus, as illustrated in Example VIII, the addition of a certain amount of dodecanedioic acid to the sebacic acid enhances the crimp retraction. This increased crimp retraction is highly desirable for sheath-core filaments Where it is difficult to obtain the retraction required for optimum results in miniature stretch hose. This procedure may also be used in the production of side-by-side filaments, however, it is usually unnecessary since side-by-side filaments characteristically develop a higher crimp than do sheath-core filaments. The maximum amount of dodecanedioic, undecanedioic, or other dibasic acid permissible in the acid mixture is dictated only by the effect on the crystallinity of the copolymer component since too large an amount may inhibit crystallization. Where mixtures of. closely related acids are employed (see Examples I and VIII) in forming one portion of the copolymer for this invention, the individual identities are not considered and all acids (and resulting polymers) are considered to be the major acid present in determining whether the requisite minimum of 20 percent of each of two polymer units is present. This course is followed where a mere technical grade of acid is employed (Example I, where the 8% of 11 and 12 carbon atom acids are considered as sebacic acid) or where a substantial acid addition is made (Example VIII) to provide enhanced properties. It is also to be noted in the production of sheath-core filaments where high crimp retraction is required, it is desirable that the core polymer have a higher relative viscosity than the sheath polymer.

In order to provide hose which have the necessary ability to stretch, the filament must have the ability to i crinrp, i.e., have the necessary retractive force when subjected to the tension imposed by the fabric construction. This tension has been found to be about 0.001 g.p.d. Therefore, a filament which has a crimp retraction value of at least 12%, preferably 1230%, in atmospheric steam and i at least 24% in 118 C. steam after being crimped under a tension of 0.0012 g.p.d., is entirely satisfactory in knit fabrics such as hosiery leg yarn. Sheath-core yarns with at least 6.5% crimp retraction in atmospheric steam are satisfactory for hosiery welt yarns.

The wearer of a stocking experiences comfortable fit sensation when stresses from the strained fabric at the ankle and at the knee are satisfactory. Laboratory determination of such stress-strain relationships are made on a hosiery beam stretch-tester. This tester holds taut a stocking at the outside extremities of the welt and of the sole, while stress-strain measurements are taken with a twoarmed probe inserted inside of the stocking. The first arm of the probe does not move within the stocking, and the second (contiguous with the first arm) is supported on a fulcrum. The inside ends of both arms are in juxtaposition when the apparatus is not loaded. When a proper load (weight) is applied to the outside end of the second arm, the stocking is placed in tension locally by the two inside ends. The distance separating the two inside ends is a function of the weight applied, so that the stress-strain relationship is thereby determined. Test results indicate that a stocking constructed with the filaments of this invention has a comfortable tension not only at the knee but also a comfortable tension at the ankle, the ankle tension being more than twice that of conventional stretch hose.

In connection with the requisite minimum value of 12% crimpretraction in atmospheric steam and 24% retraction at 118 C. for leg yarns, it has been found that the various crimpable, side-by-side or sheath-core composite filaments disclosed in the prior art do not have sufiiciently high crimp retraciion values and do not provide the necessary degree of crimping under the tension which is necessarily imposed in the knit fabric. For example, copolymers such as 50:50 6-6/ 6 nylon which do not crystallize or develop a crystalrlike structure usually shrink sufficiently to produce a relatively high crimp in the' composite filament but the crimp refractive force is insufficient to permit such a filament to crimp to the desired degree after its incorporation into a fabric. Thus, copolymers which do not give indications of crystallinity when heated in a relaxed or semi-relaxed condition are not satisfactory. Similarly, when one component consists of 6-6/PVP (10-30% polyvinyl pyrrolidone), the resulting composite filament does not have sufficient shrinkage to develop adequate crimp when under tension. In higher percentage concentrations of PVP, the filaments are further deficient in that they do not have sufficient strength. Other copolymers which have been found to be inoperable are those which are isomorphic, e.g., those prepared from hexamethylene diamine with adipic and terephthalic acids or from hexamethylene diamine and p-xylylene diamine with adipic acid (30% PXD-6). Another inoperable copolymer is that prepared from hexamethylene diamine with piperazyl-bis-N,N-pentanoic and adipic acids (50% 6-5 pip 5). Similarly, the terpolymer 6-6/6-10/6 is inoperable in 50:25:25, :2:13 and 44:28:28 ratios. Other two-component filaments consisting of two homopolyamides (e.g., 6-6 and 6, 6-8 or 6-10) are not suitable since they do not have a sufficiently high shrinkage differential to generate the necessary crimp retractive force to provide a crimp retraction of at least 12% in atmospheric steam and 24% at 118 C. under a restraint of 0.0012 g.p.d.

For use in hosiery leg yarn, the preferred two-component filaments are those having a crimp helix diameter of about 6-11 mils (optimum 7-11 mils) and a helix spacing of about 16-50 mils (optimum 24-38 mils) when crimped in 118 C. steam since this type crimp gives a uniformly rounded stitch in the hose and consequently a much better appearance.

As recorded in Examples I and VI, the 6-6/6-10 and 6-6/6-12 copolymers develop a crystal-like structure and exhibit X-ray diffraction characteristics similar to those of 6-6 nylon but, because of the differences in chemical repeat distance (or spacing of hydrogen bonds in the crystal structure), it is not believed that such a copolymer system can form a truly crystalline structure. It is theorized that the crystallinity indications observed in the 6-6/6-10 copolymer results from the formation of sheets of 6-6 polymer chains and other sheets of 6-10 polymer chains, the sheets being stacked in a regular fashion and held together by van der Waals forces while the polymer chains within the sheets are held together by hydrogen bonds. In connection with the 6-6/6-1 copolymer of Example V, it is theorized that the crystallinity indications are those of the 6-6 units in the copolymer and that the 6-I structure is not such as to interfere with the crystalline behavior of the 6-6 in the concentrations employed.

In addition to the copolymers exemplified, other crystallizable, nonisomorphic copolymers in which the 6-6 polymer units are replaced with units such as octamethylene oxamide (8-2), tetramethylene subcramide (4-8),

13 hexamethylene suberamide (6-8), decamethylene sebacamide (10-10), p-xylylene azelamide (PXD9), 2-methylhexamethyleneoxamide and epsilon-caproamide may be employed.

The homopolyamide component in the composite filament must be crystallized. Otherwise, the shrinkage of this component may be so high that the necessary shrinkage difierential between the two components will not be achieved. Crystallization and orientation of this component should take place to a substantial degree by the end of the drawing step in order to insure the desired relatively low shrinkage rate in the subsequent crimping step. This component should consist essentially of the homopolyamide but the addition of another polymer as a melt blend or another copolyamide in a very small amount obviously would not seriously impair its function. Suitable :crystallizable homopolyamides in addition to those exemplified include: polyheptanamide, polyundecanamide, polyoctamethylene oxamide, polytetramethylene suberamide, polyhexamethylene suberamide, polyxylylene azelamide and poly-2-methyl-hexamethylene terephthalamide. Crystallizable isomorphic copolymers such as the copolymer of polyhexamethylene adiparnide and polyhexamethylene terephthalamide may be used in place of the homopolyamide component.

Both components of the filament of this invention must be extruded from polymer of fiber-forming molecular weight in order to avoid processing ditficulties and provide filaments which have satisfactory crimpability. In side-by-side extrusion the use of a low molecular weight component leads to bending of the filaments as they emerge from the spinneret orifice ond commercial operability is not obtained. In either side-by-side or sheathcore extrusion, it is found that the surface tensions of the two molten polymers must be approximately equal to obtain filaments having the desired high crimping force. For practical production of hosiery filaments, one component must have a relative viscosity of at least about 35 at extrusion in order to avoid severe processing difficulties. Preferably, the two components differ in relative viscosity by no more than 10 units.

In the extrusion of sheath-core filaments, the homopolyamide is preferably extruded as the sheath to facilitate quenching of the filaments. Use of the copolyamide as the sheath results in slower quenching, frequently leads to filament sticking at high spinning speeds and results in excessive broken filaments during drawing. Where side-by-side filaments are extruded the filaments from a single spinneret should be similarly oriented with respect to the position of the components to insure uniform exposure to the quenching air which is usually blown across the filaments. Preferably the copolyamide component is on the side from which the quenching gas is blown.

The two components are preferably present in approximately equal amounts by weight of the filaments in sideby-side structures. However, with sheath-core filaments it may be desirable to employ a somewhat larger percentage of the higher shrinkage component. When the components are present in a ratio other than about 50:50, it is preferable that the copolyamide component be the greater of the two since it is the higher shrinkage component and therefore provides the necessary retractive force to produce crimping.

In producing sheath-core filaments, the core should be highly eccentric as illustrated in Example VII in order to develop the required retractive force on crimping. This means that part of the sheath will be very thin, i.e., the minimum thickness of the sheath will range from of the filament diameter to 0.1% or less and is preferably no more than about 2% of the filament diameter.

In order to produce the requisite structure in the composite filament, it must be drawn under conditions which do not cause crystallization of the copolyamide to a substantial degree and, after drawing, it must be heated in a relaxed or partially relaxed state to crimp the filament and crystallize the copolyamide, and then cooled to con solidate the structure. The filament may be cold drawn or drawn at moderately elevated temperatures provided that the temperature is not sufficient to cause appreciable crystallization of the copolymer. The temperature, heating time and degree of relaxation required in the relaxation step may vary somewhat depending on the polymer systern employed. The optimum conditions for drawing and relaxation are easily selected by one skilled in the art. In general the filaments should be heated in the relaxation step at a temperature of at least C. but below the softening point of either of the components for a sutficient time to permit development of the crystalline structure. Where the filament is heated in a completely relaxed state or under very slight tension, the time is adjusted to permit the maximum degree of crimp to develop in the filament. In addition to high-temperature air, steam may also be employed as the heating medium and may be preferred with higher filament deniers and higher processing speeds.

After the filament is permitted to crimp in the relaxed heat treatment, it should be cooled to set the structure and the crimp removed by stretching. The stretching may also be adjusted to produce the desired degree of crimping when the filament is subsequently crimped in the fabric. Where snubbing pins are used in the stretching operation as illustrated in the drawings, application of a high friction finish to the filaments is desirable.

The relaxation step also serves to reduce the shrinkage of the filament which takes place before crimp is formed in the fabric. In hosiery yarn, a shrinkage in boiling water in excess of 15% in the leg yarn is undesirable and lower shrinkages are required in the welt yarn. A heater may be provided integral with the crimping chamber to heat the crimping fluid to the pre-determined temperature. To overcome the problem of temperature rise due to the loss of windage and yarn heat absorption in this type of apparatus when the winding of the yarn is stopped, a commercially available limited range transformer may be installed in the electrical circuit to compensatively reduce voltage to the heater when the winding is stopped.

In addition to the yarns exemplified, other deniers such as 20, 25 and 30 denier monofils for hosiery, leg yarn may be produced in accordance with this invention. A 20-denier filament, for instance, gives improved yarn processability and improved durability in hose while a 30-denier filament can be processed into hose which exhibit sufficient compressive force on the leg to qualify as support hose while having a much better appearance than regular support hose. The number of filaments may be varied also if desired. Yarns such as 15 denier 2 filament, 21 denier 3 filament and 20 denier 2 filament may be used for hosiery leg yarn while yarns such as 30 denier 1O filament, 45 denier 7 filament and 50 denier 10 filament may be used in the welt and foot sections. Although hosiery filaments are usually of round cross section, other shapes can be employed for hosiery or other products and may indeed be particularly useful in certain end uses such as in tricot knit fabrics or certain woven fabrics. For such purposes, cross sections of trilobal shape as disclosed and claimed in U.S. 2,939,201 or shield shape as in US. 2,939,202 may be employed as may others such as heart shape, cruciform shape, and various multilobal configurations. Either side-by-side or sheath-core filaments can be produced in any of the above shapes.

The filaments of this invention are particularly adapted for use in the production of stretch-type hosiery. Hosiery prepared from these filaments are equivalent in fit and comfort to commercially available stretch hose but are far superior in appearance due to the clarity of stitch and more normal size and shape as compared to the small, oddly-shaped stretch hose currently available. By employing appropriate hose finishing conditions, these filaments may also be used to prepare miniature hose which are superior to those currently available in stitch clarity and general appearance on the leg. In addition to their use in ladies hosiery, these filaments may also be used to advantage in sweaters, stretch tricot fabrics, mens hose and woven fabrics.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A crimpable, drawn, heat-relaxed-stretched, composite, nylon filament comprising continuous, adherent, eccentric, fiber-forming components of a crystalline homopolyamide and a nonisomorphic random copolyamide, said copolyamide component containing at least by weight of each of two polymer units and exhibiting crystallinity evidence by X-ray diffraction characteristics substantially similar to those of the homopolyamide component, said filament being crimpable into a helical configuration upon exposure to a heated atmosphere and having a crimp retraction of at least 24% when crimped in a 118 C. steam atmosphere under a restraint of 0.0012 g.p.d.

2. A fabric knitted from a plurality of the crimpable filaments of claim 1 and then heated to develop crimp in the filaments.

3. The crimpable filament of claim 1 wherein said homopolyamide is polyhexamethylene adipamide and said copolyamide contains at least 20% by weight each of polyhexamethylene adipamide and polyhexamethylene sebacamide units, said filament having when crimped a crimp helix diameter of 6-15 mils and a crimp helix spacing of l670 mils.

-4. A crimpable, drawn, heat-relaxed-stretched, composite, nylon filament comprising continuous, adherent, eccentric, fiber-forming components of a crystalline homopolyamide and a random copolymer containing at least 20% by weight of polyhexamethylene adipamide units and at least 20% by weight of polymer units selected from the group consisting of polyhexamethylene sebacamide, polyhexamethylene dodecanedioamide and polyhexamethylene isophthalamide, said copolymer component exhibiting crystallinity evidenced by X-ray diffraction characteristics similar to those of the homopolyamide component in that a radial densitometer trace shows distant peaks in equatorial reflections, said filament being crimpable upon exposure to a heated atmosphere and having a crimp retraction of at least 24% when crimped in a 118 C. steam atmosphere under a restraint of 0.0012 g.p.d. and said homopolyamide being selected from the group consisting of polyhexamethylene adipamide and polycaproamide.

5. The filament of claim 4 wherein said copolymer component contains from 70% polyhexamethylene sebacamide units.

'6. The filament of claim 4 wherein said copolymer component contains from 2040% polyhexamethylene isophthalamide units.

7. The filament of claim 4 wherein said copolymer component contains from 40-60% polyhexamethylene dodecanediamide units.

8. A fabric knitted from a plurality of the crimpable 16 filaments of claim '4 and then heated to develop crimp in the filaments.

9. A crimpable, drawn, heat-relaxed-stretched, composite, nylon filament comprising continuous, adherent, eccentric, fiber-forming components of a crystalline homopolyamide and a nonisomorphic random copolyamide, said copolyamide component containing at least 20% by weight of each of two polymer units and exhibiting X-ray diffraction characteristics substantially similar to those of the homopolyamide component in that a radial densitometer trace shows distinct peaks in equatorial reflections, said filament having a crimp retraction of at least 24% when crimped in a 118 C. steam atmosphere under a restraint of 0.0012 g.p.d., said filament when crimped being in a helical configuration with a crimp diameter of 6 to 15 mils and a crimp helix spacing of 16 to mils.

10. The filament of claim '9 in which the crimp diameter in said helical configuration is 7 to 11 mils and the crimp helix spacing is 16 to 38 mils.

11. A crimpable, drawn, heat-relaxed stretched, composite, nylon filament comprising continuous, adherent, eccentric, fiberforming components of a crystalline homopolyamide and a random copolymer containing at least 20% by weight of polyhexamethylene adipamide units and at least 20% by weight total of polyhexamethylene sebacamide, polyhexamethylene dodecanediamide and polyhexamethylene undecanediamide units, said copolymer component exhibiting crystallinity evidenced by X- ray diifraction characteristics similar to those of the homopolyamide component in that a radial densitometer trace shows distinct peaks in equatorial reflections and is characterized by a peak separation ratio of at least 1.10, said filament being crimpable upon exposure to a heated atmosphere and having a crimp retraction of at least 24% when crimped in a 118 C. steam atmosphere under a restraint of 0.0012 g.p.d. and said homopolyamide being selected from the group consisting of polyhexamethylene adipamide and polycaproamide.

12. The crimpable filament of claim 9 wherein said homopolyamide consists essentially of polyhexamethylene adipamide, said random copolyamide consists essentially of polyhexamethylene adipamide/sebacamide/undecanedioamide/dodecanedi0amide units, and said components are arranged in a sheath-core relationship with the copolyamide in the core.

13. The crimpable filament of claim 12 wherein the components have about the same relative viscosity and one component has a relative viscosity of at least 35.

References Cited UNITED STATES PATENTS 2,987,797 6/1961 Breen 16l175 3,046,257 7/1962 Evans et al 26078 3,038,235 6/1962 Zimmerman 16ll73 ROBERT F. BURNETT, Primary Examiner.

L. M. CARLIN, Assistant Examiner. 

